I have a 5-button mechanical combination lock gun safe that works great. It's very fast to open, and short of taking a torch and crowbar to it, it will not open unless you know the combination. Mine was made by AMSEC (15 years ago), but it appears that all new AMSEC models have electronic locks, which I wouldn't trust, for the reasons mapsjanhere stated. V-Line does make a
Compact Safe that appears to be similar to mine. I'm sure there are similar ones made by other manufacturers.
What I like about the 5-button combination lock is that your combination can be made more-difficult to guess by requiring some of the buttons to be pushed simultaneously. For example, my combination (which is disguised--not my real combination) consists of buttons 4 and 5 pushed simultaneously, followed by buttons 1 and 3 pushed simultaneously. I've practiced to the point that I can enter my combination and open the box in one second (even in the dark).
DogoDon